Perceiving Plant Steroids

Genome analysis of Arabidopsis and other plants has identified a family of proteins that share leucine-rich repeats and have other characteristics that suggest that they may be receptor-like kinases. He et al. now present an analysis of one family member, BRI1, previously implicated in brassinosteroid signaling. They worked with a fusion protein constructed from the extracellular domain from the Arabidopsis protein and the kinase domain from a receptor from rice that modulates disease resistance. They now show that the perception of the ligand, in this case a steroid, occurs through the extracellular domain of BRI1, at the cell surface.